1. Field of the Invention
The invention relates to high voltage power cable for ultra deep waters applications.
2. Description of the Related Art
Ultra deep waters can be considered as being at least 3000 meters under the sea level. At such depths, deep waters applications will induce large tensile strain on the cable. The weak element in high voltage power cable application is the metallic conductors, generally consisted of copper, due to their poor mechanical properties, and especially due to their poor elongation capacity. During installation and service, the high voltage power cable will be exposed to large tensile forces and dynamic motion which will induce fatigue problems. The metallic conductors, especially when they are made of copper material, will be damaged when they are exposed to an elongation above a critical limit. Such damage phenomena can be explained by the fact that high voltage power cable comprises an armour package with an elongation capacity of 0.3% or more, and insulated metallic conductors with a poor elongation capacity of approximately 0.1%. Consequently, when the high voltage power cable is exposed to large tensile forces, only 30% of load bearing capacity of the armour package can be used without reaching an unacceptable elongation in the metallic conductors. Due to this, it is necessary to increase the elongation capacity of the insulated metallic conductors, in order to use 100% of the load bearing capacity of the armour package and to have acceptable tensile load in the insulated metallic conductors. Hence by increasing the elongation capacity of the metallic conductors we can reach significant larger water depths.
Such cables used in deep water applications and conceived to withstand tensile forces, have been already developed and patented. For instance, EP 1691378 discloses an electrical signal cable, comprising at least two insulated conductors, and of which the main technical feature is that each of the insulated conductors is arranged in a groove of a longitudinal central element consisting of an elastic material which allows the insulated conductors to move in radial direction of the said cable when the latter is exposed to longitudinal tensile stress. The cable is surrounded by a sheath of insulated material, and the elastic material fills entirely the space inside the said sheath so that it is in contact with this sheath along its circumference, except the areas corresponding to the grooves. In other words, the insulated conductors are totally embedded inside the elastic material. This invention presents two drawbacks which are, in one hand, that each insulated conductor cannot move freely inside the electrical signal cable when exposed to large tensile forces, and on the other hand, that no device is designed inside the cable to better distribute the radial forces, so that the said cable be able to better withstand the loads.
The high voltage power cables according to the invention are designed to increase the elongation capacity of the metallic insulated conductors without the two drawbacks mentioned before. This way, they are well adapted to ultra deep waters applications by improving their resistance to very high pressure without damaging the said insulated metallic conductors.